This invention relates to a plastic stopper for a receptacle, with the stopper comprising a cover member with a circumferential wall which encompasses the neck of the receptacle and whose lower edge has molded thereon a surrounding tear-off sealing ring for ensuring the original state of the contents of the receptacle with inwardly oriented blocking attachments which grip below an outwardly facing annular projection of the receptacle in the secured position of the stopper.
The present invention also relates to a method for making such a stopper.
EP 0 202 506 A2 discloses a stopper whose sealing ring has molded thereon tabs which are oriented obliquely inwardly and into the stopper opening direction and which grip below a flanged edge of the receptacle. This stopper can be removed from the receptacle neck without damage to the predetermined break seam of the sealing ring if suitable tools are introduced below the sealing ring, and the tabs press against the sealing ring, whereupon the stopper can be removed from the neck of the receptacle. Such an unauthorized procedure requires some skill, but is possible in principle.
The prior-art stopper is produced with the aid of an injection mold with so-called dipping cores which grip behind the obliquely upwardly oriented tabs. Such a crown insert which is in permanent contact with the inner mold core and performs a relative movement with the latter tends to form undesired ridges and has a short service life. As a consequence, it must be replaced frequently. Apart from the increased material costs, the resultant idle times raise the production costs.
Moreover, recesses through which the dipping cores pass are provided in the cover portion of the prior-art stopper. Although these recesses are radially outside the receptacle opening, they permit the entry of foreign matter on the neck portion of the receptacle.